1. Field of the Invention
The present invention relates to a biaxially blow-molded bottle-shaped container made of synthetic resin, more particularly to a construction of a body portion of a biaxially blow-molded bottle-shaped container made of polyethylene terephthalate resin.
2. Prior Art
There has hitherto been widely used a bottle-shaped container which is produced by biaxially blow-molding a preformed parison of synthetic resin such as polyethylene terephthalate resin. Such a bottle-shaped container has an excellent resistance to contents which is provided by sufficiently orienting the preformed parison. The bottle-shaped container is formed with a thin wall and is light. The container has an excellent shock resistance and can be inexpensively produced by mass production.
However, there is a problem that when the bottle-shaped container is filled with a hot liquid content and subsequently cooled, the wall of the body portion of the bottle-shaped container is deformed owing to a reduced pressure in the container.
Accordingly, there has been known to provide panel walls in the body portion to absorb the reduced pressure by an elastic deformation of the panel walls. It is required that each panel wall is relatively large flat wall construction due to the following reasons. (1) By the reduced pressure, the panel wall is more deformable than the rest of the body portion. (2) The depression deformation occurring on the panel wall is an elastic deformation. (3) Only a little depression-deformation decreases the volume of the container a large amount.
A large biaxially blow-molded bottle-shaped container having a cylindrical body portion of a circular section can be provided with reduced-pressure absorbing panels only by forming vertically extended flat portions on the peripheral surface portion of the body portion. Therefore, the shape of the panel walls on the body portion of the container is vertically elongated and as a result, the panel walls of the container cannot be greatly deformed. Therefore, the volume of the bottle-shaped container does not greatly vary by the depression-deformation of the panel walls on the body portion of the bottle-shaped container.
A large biaxially blow-molded bottle-shaped container having a cylindrical body of a square section can be provided with reduced-pressure absorbing panels by forming a flat portion on each side of the square cylindrical body portion. Each flat portion can be easily and sufficiently deformed and has a large flat area so that the volume of the container can be greatly varied by the deformation of the flat portions. Thus, each flat portion effectively acts as a panel wall for absorbing the reduced pressure.
FIG. 3 illustrates a conventional bottle-shaped container 1' having a square cylindrical body portion 2'. Each side surface of the body portion 2' continues to adjacent both side surfaces through ridge line portions, respectively. Each side surface of the body portion is provided with a reduced-pressure absorbing panel wall 3' for absorbing the deformation of the wall of the bottle-shaped container caused by the reduction of the pressure in the container.
When the pressure in the bottle-shaped container 1' is reduced, the panel wall 3' is deformed and inwardly bent to cause an internal stress extended to the ridge line portions. The ridge portions are pillar portions for maintaining the shape of the bottle-shaped container and must have a high mechanical strength. If the ridge portions are deformed by the internal stress, the mode of bending of the panel wall 3' is not constant and the body portion of the square cylindrical shape is deformed. In particular, large bottle-shaped containers are greatly deformed by the reduced pressure, because the large bottle-shaped containers have a thin wall owing to a deep orientation and a large height thereof. Thus, the large bottle-shaped containers are required to have ridge line portions having a high mechanical strength.
In order to eliminate the aforementioned problems, there has been designed to provide elongated grooves 5' in the ridge line portions. Such an elongated groove 5' acts as a reinforcing rib to increase the mechanical strength in the ridge line portion to thereby prevent the ridge line portion from undue strain deforming owing to the deformation of the panel wall 3'.
Generally, biaxially blow-molded bottle-shaped containers produced in a factory are packed in cases made of a corrugated cardboard and transported to other factories for filling liquid into the bottle-shaped containers. The bottle-shaped container is light, but is bulky. Consequently, in order to efficiently transport the bottle-shaped containers, it is desirable that a number of bottle-shaped containers are closely packed in each cardboard case.
However, when uncapped bottle-shaped containers as shown in FIG. 3 are closely packed within the cardboard case and are subjected to an external pressing force over a limit of the resistance force of the ridge line portions having a mechanical strength sustained by the elongated grooves 5', the ridge line portions are inwardly bent to result in a bending deformation. This bending-deformation is semi-permanently since the elongated grooves 5' act as reinforcing ribs in the condition of bending deformation to prevent the ridge line portions from elastically returning back to the original form.